1. Field of the Invention
The present invention generally relates to optical detectors, and more particularly, to high bandwidth monolithic optical detectors formed on a semiconductor opto-electronic integrated circuit.
2. Description of the Related Art
The increasing use of fiber optic computer communications has created a need for inexpensive high speed optical receivers. In particular, receivers using opto-electronic integrated circuit (OEIC) techniques in which the photo diodes are fabricated on the same chip as the electronic circuitry are desirable because of the resulting reduction in packaging and testing costs. At wavelengths less than about 870 nanometers (nm) metal-semiconductor-metal photo detectors can be formed on a substrate along with GaAs MESFET circuitry.
It is also desirable to form such detectors on a silicon substrate in order to take advantage of the lower manufacturing costs associated with silicon fabrication. However, the long optical absorption length for silicon at wavelengths of about 850 nm is prohibitive. This absorption length, which is about 12 .mu.m, requires relatively thick layers of high resistivity silicon to absorb an appreciable amount of incident light. Unfortunately, such thick layers are not available in the device portion of standard silicon integrated circuit processes. Further, the long absorption length also leads to long transit times for electrons and holes to move through these layers, thereby limiting the frequency response of prior art silicon detectors.
Accordingly, there remains a need for an optical detector design which is compatible with current silicon manufacturing technology and offers sufficient bandwidth to be useful in high speed optical communications applications.